Hitherto the nickel alloy having Material No. 2.4856 in the Iron and Steel List of the Verein deutscher Eisenhuttenleute has been used for articles which must be resistant to carbonization, sulphidization and oxidation in the temperature range of 500 .degree. to 1000.degree. C., more particularly with cyclic stressing. The alloy consists of (in % by weight) max. 0.10% carbon, max. 0.5% silicon, max. 0 5% manganese, 20-23% chromium, 8-10% molybdenum, 3.15-4.15% niobium, max. 0 4% titanium, max 0.4% aluminium, residue nickel. However, in heavily carbonizing conditions this standard alloy shows heavy carbonization at temperatures above 900.degree. C., taking the form of a distant increase in weight due to heavy carbide precipitations and carbon absorption. As a result the mechanical properties, more particularly long-term strength, are also unfavourably affected thereby. The standard alloy shows clear damage due to sulphur absorption even in oxidizing/sulphidizing conditions such as, for example, a gaseous atmosphere of nitrogen and 10% SO.sub.2 at 750.degree. C.
The austenitic steel disclosed in EP 0 135 321 containing (details in % by weight) max. 0.03% carbon, 20-35% chromium, 17-50% nobium and 2-6% silicon, is as a result of its high silicon content resistant to corrosion in heavily oxidizing mineral acids, such as nitric acid, but it is unsuitable for use at temperatures above 500.degree. C. in carbonizing, sulphidizing and oxidizing conditions.